1. Field of the Invention
The invention relates to a method and a device for determining a frequency mask for a frequency spectrum.
2. Related Technology
In the analysis of the frequency spectrum of a signal to be detected using a spectrum analyzer, frequency masks are used. In this context, an upper and lower frequency mask is defined, which marks the validity region of the frequency spectrum to be analyzed. If the frequency spectrum is disposed completely within the upper and lower frequency mask, a valid frequency spectrum is accordingly available. By contrast, if the frequency spectrum is disposed at least partially outside the upper and/or lower frequency mask, the spectrum analyzer initiates a triggering or a data collection or a marking of the recorded data record followed by a display of the invalid frequency region at a detection time or over a detection time interval on the display. Additionally, in a case of an invalidity, the spectrum analyzer can also issue a warning, for example, an error message or an acoustic signal.
The upper and lower frequency mask is entered manually by the user of the spectrum analyzer through a graphic entry of the curve characteristics of the upper and lower frequency mask or through an alphanumeric entry of curve-characteristic values of the upper and lower frequency mask on a graphic or alphanumeric user surface of the spectrum analyzer. In the case of a semiautomatic entry, the user of the spectrum analyzer is shown a menu with a given number of parametrisable curve characteristics for the upper and lower frequency mask for selection and subsequent parametrisation. With a fully automatic generation of the frequency mask, an upper and/or lower frequency mask suitable for the analysis of the frequency spectrum is determined by the spectrum analyzer without the involvement of the user starting from the detected frequency spectrum.
An automatic generation of a frequency mask of this kind for a detected frequency spectrum is known from EP 2 071 341 A2. For this purpose, the detected frequency spectrum is displaced in both frequency directions in each case by a given frequency value. If the two frequency spectra displaced respectively by a given frequency value in positive and negative frequency directions are connected to one another horizontally at the respective dividing points and displaced vertically upwardly and/or downwardly by multiplication in each case by an appropriate amplification factor, an upper and/or lower frequency mask that is distanced from the detected frequency spectrum in the horizontal and also in the vertical direction is obtained. The frequency value by which the detected frequency spectrum is displaced in the horizontal direction, and the amplification factor, by which the horizontally displaced frequency spectrum is displaced vertically can be predetermined by the user and determine the size of the tolerance band between the detected frequency spectrum and the upper and lower frequency mask.
While a frequency mask for a frequency spectrum with singular and clearly distanced spectral components which approximates the frequency spectrum relatively well within a given tolerance distance is generated according to this prior art, the known method fails with a frequency spectrum with closely adjacent spectral turning points in the spectral characteristic, that is to say, with turning points in the spectral characteristic which are disposed within the frequency value by which the original frequency spectrum is displaced in the horizontal direction.